1. Field of the Invention
The present invention relates to a parts mounting method and parts mounting apparatus, used for mounting electronic parts onto a board or the like.
2. Description of the Related Art
Conventionally, for mounting electronic parts such as semiconductor chips, piezoelectric devices, or the like, on a board such as a printed board, a positioning mechanism with high precision is necessary for mounting such electronic parts at predetermined positions on the board.
Such a positioning mechanism is disclosed in Japanese Patent No. 2,780,000 and another mechanism is disclosed in Japanese Patent No. 2,811,856. With the mechanism disclosed in Japanese Patent No. 2,780,000, two cameras take images of a specific mark from above and from below, respectively, so as to detect the offset between a workpiece and a board, and correction is performed for the relative movement amount between the workpiece and the board based upon the detected offset. On the other hand, Japanese Patent No. 2,811,856 discloses a method wherein cameras are inserted into a position on a line formed between the board and an electronic part for taking images upward and downward at the same time, i.e. a method wherein back-to-back cameras take images upward and downward at the same time.
However, with the positioning mechanism disclosed in the Japanese Patent No. 2,780,000, an axial mechanism with highly-precise repeatability is necessary for moving the workpiece and the board, and furthermore, the offset between the workpiece and the board cannot be detected at the time of bonding. Furthermore, correction using the specific mark is performed for detecting the relative positional offset between the upper camera and the lower camera, and accordingly, the margin of error with regard to the distance between the upper camera and the bonding unit due to thermal expansion or the like, and the margin of error with regard to distance between the lower camera and the bonding stage due to thermal effects or the like, cannot be detected, and consequently, there is a limit to the amount of improvement of precision that is available with regard to bonding.
On the other hand, with the mechanism disclosed in Japanese Patent No. 2,811,856, the back-to-back cameras are inserted into a position in alignment with the workpiece and the board so as to detect the offset therebetween, and accordingly, there is the need to retract the back-to-back cameras to one side from this position in the alignment at the time of bonding, so the positions of the workpiece and the board cannot be detected at the time of mounting. Furthermore, since the cameras have back-to-back fields of view, the cameras cannot have the same field of view in principle for taking an image of a single calibration mark, leading to the problem that the positioning of these two cameras requires a complex operation.